With increasing development of digital technology and communication technology, multimedia content based on audio/video (A/V) data has rapidly come into widespread use in various technical regions (e.g., broadcasts, movies, Internet, personal media, etc.) and the number of users who desire to use multimedia content is also rapidly increasing. In addition, with widespread use of 3DTV/3D movies capable of providing users with a stereoscopic three-dimensional (3D) effect, immersive media capable of providing the users with the 3D effect and stereo sound is rapidly increasing. In addition, as the TV screen is gradually increased in size in proportion to the increasing development of display technology, the number of users who desire high-quality content such as high definition (HD) content is also rapidly increasing. Therefore, many developers and companies are conducting intensive research into technology of immersive broadcasting TVs (such as 3DTVs and UHDTVs (Ultra High Definition TVs)) as next generation broadcast services to prepare for the Post-HDTV market. Specifically, in recent times, a variety of research into UHD (Ultra High Definition) broadcast services has been developed.
With increasing development of UHD displays and transceivers, UHD services have been intensively researched. An ultra high definition (UHD) broadcast may be distinguished from a legacy broadcast and provide a high sense of realism, by expressing colors and/or brightness which cannot be expressed in legacy content. However, many developers and companies are conducting intensive research into Wide Color Gamut (WCG) and/or High Dynamic Range (HDR) images and display devices for displaying WCG and/or HDR images.
UHD broadcasting aims to provide TV viewers with higher-quality images, higher-quality colors, and higher sense of immersion in a wider variety of aspects than conventional HD broadcasting. Therefore, a UHD broadcast associated standard has recently been established to define wider color gamut than in conventional TVs. UHD content can provide TV viewers with the best information similar to the original color directly obtained through HVS (Human Visual System), such that it can provide the TV viewers with higher-quality images and a greater sense of immersion. Although the current broadcast system is designed to perform various post-processing steps needed to implement color enhancement, prior to transmission of the content for optimum color implementation, the current broadcast system has difficulty in perfectly expressing various colors due to a difference in environment between the actual display environment of each user and the manufacturing environment of the content manufacturer. In order to provide improved broadcast services in UHD broadcast in a different way from the legacy HD broadcast, there have been intensively discussed various technologies for providing TV viewers with immersive content and a high sense of realism in various technical aspects. As a representative method for creating the content brightness expression range similar to visual sense of the TV viewer, there is a need to discuss and study High Dynamic Range (HDR).
Since a WCG based image format standard has recently been established, it will take a long period of time to rapidly spread WCG based image acquisition devices and WCG based display devices. Therefore, UHD service transmission standards will be established in consideration of future compatibility. In this case, video data having legacy color gamut may be supplied using the WCG transmission format. For this purpose, a method for providing a high-quality service in consideration of the display environment through proper processing of a receiver is needed.
In legacy analog broadcasting and SDTV/HDTV, the standard color gamut has been established simultaneously with development of video service technology, such that the same color gamut has been used in image acquisition, post-processing, transmission, and display in legacy analog broadcasting and SDTV/HDTV. In other words, a color gamut matching a target service is present. Thus, if a production and/or a transmitter performs post-processing on the basis of the matched color gamut and transmits the post-processed result, a difference in color gamut between respective steps need not be considered. However, various color gamuts have been considered in UHD, for example, REC.709 currently used in HDTVs, BT.2020 established as UHDTV standard, DCI-P3 including an intermediate range of HDTV and UHDTV, xvYCC, etc. The legacy image acquisition devices support only REC.709 based color gamuts, and the legacy display supports only REC.709 based images. As described above, it will takes a long period of time to introduce BT.2020 into the image acquisition device and the output device. In this case, considering the future compatibility problems, there is a need to research and develop services capable of supporting the above-mentioned two cases in a single broadcast service.